Influence of dietary fiber on fecal excretion of volatile fatty acids by human adults.

The ability of dietary fibers to influence the excretion of volatile fatty acids (VFA) in feces was evaluated in five healthy men. Throughout the 63-day study subjects were confined to a metabolic unit and fed semipurified diets. Each diet was consumed for 9 days. Feces were homogenized, and aliquots were analyzed for VFA by a steam distillation procedure followed by gas-liquid chromatography. Individuals showed wide variability in the extent to which they excreted VFA, and there is evidence of some subject-diet interaction. Acetate, propionate and butyrate were generally present in the ratios of 35:25:20, but the proportion of acetate was increased when xylan and corn bran were consumed. The excretion of VFA during the last 3 days of each metabolic period increased with diet as follows: xylan, fiber free, cellulose, pectin and corn bran. Corn bran caused a significant increase in total VFA excretion over the fiber-free diet. Concentration of VFA in excreted feces (or expressed as percentage of fecal solids) increased by diet in the following order: cellulose, xylan, corn bran, pectin and fiber free. Thus, the concentration of VFA in feces showed no relationship to the total quantity of VFA excreted.